The present invention relates to a dielectric gas mixture for use in electrically insulating a conductor.
When high voltages exist between the conductors of electrical apparatus (e.g., transformers, circuit breakers, or switches) arcing or sparking may take place. To prevent this phenomenon, dielectric fluids (gas or liquid) or solids are used to insulate the conductors.
One well-known dielectric gas is sulfur hexafluoride (SF.sub.6). While possessing good electric arc interrupting properties, it is relatively expensive, and suffers from relatively low vapor pressures at low temperature and a comparatively high freezing point.
A number of other gaseous compounds have good dielectric properties and are substantially less expensive than SF.sub.6 in the form of halogenated alkanes. Many of such gases are fluorinated hydrocarbons used as refrigerants and propellant under the Freon trademark series by DuPont. Such gases included dichlorodifluoromethane (CCl.sub.2 F.sub.2) and other alkanes substituted with both chlorine and fluorine atoms. However, during the high voltage surges, electrical discharges may occur in apparatus insulated with such gases. Under these conditions, some tend to break down and form free carbon, unless such formation is suppressed. This undesirable occurence is known as carbonization.
Suppression of carbon formation by the addition of SF.sub.6 gas and carbon dioxide (CO.sub.2) to such halogenated alkanes is disclosed in Mears et al. U.S. Pat. No. 4,071,461. However, these mixtures contain SF.sub.6 and so, in some degree, are subject to the aforementioned disadvantages for using that gas.